Working machine with reduced upper mass vibrations

ABSTRACT

According to the invention, a hammer or a ramming machine for compacting soil has a crank mechanism for producing a directed vibration. The crank mechanism is coupled to a spring assembly. The parts of the crank mechanism which move back and forth linearly are made from a material with a density less than that of steel. This construction prevents vibrations which are unpleasant for the person operating the working machine from occurring.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a working machine according to the preamble ofpatent claim 1. The invention relates, in particular, to a tampingmachine for soil compaction or to a hammer.

2. Description of the Related Art

Known tamping machines of this type are designed in such a way that anupper mass receiving a motor and a crank mechanism is connected via aspring assembly to a working mass which forms essentially a working orcompacting plate. The rotational movement generated by the motor isconverted by the crank mechanism into an oscillating axial movementwhich is transmitted via the spring assembly to the working plate forsoil compaction. The upper mass comprises about two thirds and thepercussive working mass one third of the entire tamper mass, whilst thedistances covered in each case by the upper mass and the working massare in inverse proportion to one another. The order of magnitude inwhich the upper mass moves in this case is 25 to 30 mm.

The vibrations of the upper mass are transmitted via a guide handle tothe person guiding the working machine, and is very unpleasant,particularly when the work lasts a relatively long time. In thiscontext, vibrations in the horizontal or lateral direction areparticularly troublesome for the operator. By contrast, vibrations inthe vertical direction are necessary for the tamper to work efficiently.

FIG. 2 shows a known tamper of this type.

According to FIG. 2, a drive shaft 1 of the tamper is driven by a motor,not illustrated, the drive shaft driving, via a pinion 2, a crank disk 3mounted in the tamper housing and provided with external toothing.Attached to the crank disk 3 is a crank pin 4, onto which a connectingrod 5 is placed in a rotationally movable manner. The connecting rod 5is connected at its other end to a guide piston 7 in a rotationallymovable manner by means of a piston pin 6. The guide piston 7 carries apiston guide 9 formed by a steel disk and fastened by means of a nut 8.The guide piston 7 is movable axially back and forth, by means of thepiston guide 9 within a guide tube 10 belonging to the lower mass. Thisaxial direction corresponds to a vertical or working direction of themachine when it is being used.

A spring assembly 11 consisting of a plurality of springs is arranged onboth sides of the piston guide 9, the springs in each case beingsupported, on their side facing away from the piston guide 9, againstspring plates 12 fastened to the guide tube 10. In order to avoid thespring assemblies 11 being blocked together, a dampening bush 13 madefrom an elastic plastic is placed onto the guide piston 7 above thepiston guide 9, whilst a damping plug 14, likewise consisting of elasticplastic, is attached below the nut 8. When the spring assemblies 11 arehighly compressed, the dampening bush 13 and the damping plug 14 can ineach case butt onto the associated spring plate 12 with their sidefacing away from the piston guide 9. They then damp the furthercompressive movement in such a way that the situation can be avoidedwhere the spring assemblies 11 are blocked together and an excessiveimpact action is consequently exerted on the working machine.

The guide tube 10, together with the spring plates 12, belongs to theworking or lower mass of the tamper. A tamping foot, not shown in FIG.1, which serves for soil compaction may be attached to the lower mass.In order to avoid the penetration of moisture and dirt, the upper massand the lower mass are connected by means of an elastic concertina 15.

As is apparent from FIG. 2, the rotational movement of the motor isconverted into an oscillating axial movement of the guide piston 7 bythe crank mechanism by means of the crank disk 3, the crank pin 4 andthe connecting rod 5. This axial movement is transmitted via the springassemblies 11 to the guide tube 10 and consequently to the lower massand can be utilized for soil compaction.

In order to damp the vibrations acting on the operator, it has beenknown hitherto to uncouple the guide handle from the upper massmechanically by means of rubber elements. In this case, however, themounted drive motor still remains exposed to high vibrational loads. Animprovement in vibration damping can be achieved here only at a highoutlay in terms of construction.

It is therefore desirable, from the outset, to avoid vibrations of theupper mass occurring.

DE-A 19 25 870 discloses a tamper for soil compaction, with a workingmass which is driven linearly back and forth, via a double crankmechanism, by a motor belonging to an upper mass. In order to reduce thevibrations on the upper mass, two weights moveable in opposition areprovided, which superpose an oppositely directed vibration on thevibration generated by the crank mechanism. The tamper has a double-legdesign, each tamper leg being driven via its own crank mechanism. Thetamper correspondingly has a very large build and can be guided on theground only with great effort.

DE-Patent 753 502 discloses a drive device for exciting vibratorysystems. For this purpose, arms and levers coupled to one another viarubber springs are provided in a crank mechanism. In order to avoidharmful dynamic mass action in the form of forces reacting on the motorand the bearings, the mass of the arms and levers is kept as low aspossible, using materials of low specific gravity.

OBJECTS AND SUMMARY OF THE INVENTION

The object on which the invention is based, therefore, is to specify aworking machine in which vibrations of the upper mass can be avoided assoon as they occur.

The object is achieved, according to the invention, by means of aworking machine having the features of patent claim 1.

It was shown, surprisingly, that the vibrations of the upper mass can bereduced considerably if materials which are lighter than steel, that isto say have a lower density than steel, are used for producing thestructural elements of the crank mechanism which are moveable linearlyback and forth, that is to say, in particular, the connecting rod,piston pin, guide piston and piston guide. This is attributable to thefact that the mass of the upper mass is reduced due to the lower weightof the moveable components, with the result that lower forces act on theupper mass.

It is particularly advantageous if the material is an aluminum alloy ora plastic, because a particularly large reduction in mass is possiblethereby.

In the working machines known hitherto, in particular in tampers,attempts have usually been made to damp the vibrations acting on theoperator by vibrationally insulating the guide handle of the machinefrom the machine itself, for example by means of rubber elements. It wasalso known to reduce the upper-mass vibration by superposing anadditional vibration generated separately. However, it is not yet knownto reduce the vibrations as soon as they occur by the use of lightweightcomponents.

In addition to reducing the movement of the upper mass, the reduction inmass of the moved components also has the advantage of saving energy,since lower masses have to be accelerated and decelerated during eachcrank revolution. The overall weight of the machine can likewise bereduced. On account of the lower accelerative load on the drive motor,longer service lives can be achieved. On the other hand, assuming thesame power output of the motor, it is possible to use somewhat wider orheavier tamping plates, whilst at the same time ensuring the sameupper-mass movement or acceleration. Furthermore, the running noise canbe reduced. Moreover, considerable cost reductions may be expected in acorresponding production method. The essential advantage, however, isthe reduction in the hand-arm vibrations acting on the operator, therebymaking it possible to work in greater comfort.

In a particularly advantageous embodiment, the piston guide can beproduced from plastic in one piece together with a dampening bush,preferably with two dampening bushes. In addition to the mass reductionmentioned, this leads to a simplification of the production method andtherefore likewise to a cost reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other features of the invention are explained in more detailbelow with the aid of the figures, of which:

FIG. 1 shows a sectional illustration of part of a tamping machineaccording to the invention;

FIG. 1 a shows a sectional illustration of part of another embodimentaccording to the invention; and

FIG. 2 shows a part section through a known tamping machine,appropriately labeled “Prior Art”.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Since essential structural elements of the tamping machine according tothe invention as shown in FIG. 1 correspond to the known elementsalready described in connection with FIG. 2, there is no need for arenewed description. For the sake of simplification, the same referencesymbols are also used for identical components in the figures.

In contrast to the known tamper shown in FIG. 2, in the tamper accordingto the invention shown in FIG. 1, some of the structural elements of thecrank mechanism which are movable linearly back and forth are producedfrom materials which have a lower density than steel and are thereforelighter than steel. Depending on the overall size and performance of thetamper, a decision must be made, in each individual case, as to whichstructural elements must be produced from lighter materials. Inprinciple, however, in order to avoid upper mass vibrations, the aim isfor as many structural elements as possible to have a lightweightdesign.

The relevant structural elements are the connecting rod 5, the pistonpin 6, the guide piston 7 and a piston guide 16 designed according tothe invention. The crank mechanism itself consists of the crank disk 3,the crank pin 4, the connecting rod 5, the piston pin 6, the guidepiston 7 and the piston guide 16.

The connecting rod 5 may be produced preferably from plastic, forexample from carbon fiber- or glass fiber-reinforced polyamide. A glassfiber-reinforced polyamide is suitable for the guide piston 7.Alternatively, a wrought aluminum alloy could be employed for the guidepiston as indicated by the metallic piston 7 a in FIG. 1 a.

The connecting rod 5 consisting of plastic has some elasticity andtherefore spring properties. This elasticity is assisted by an o-legshape, that is to say by an arcuate run of the connecting rod 5 betweenthe crank pin 4 located on the crank disk 3 and the piston pin 6arranged on the guide piston 7. The connecting rod 5 therefore forms anoval “O”, through the center of which the drive shaft 1 extends. Thelateral legs of the “O” improve the springing or damping capacity of theconnecting rod 5, with the result that the bearings and toothings andalso other components connected to the connecting rod 5 are protected.

The piston guide 16 integrates in one component the steel piston guideknown from the prior art, the expansion bush consisting of an elasticplastic and the expansion plug. The piston guide 16 has, approximatelyin the middle, a wider edge 17, against the two sides of which thespring assemblies come to bear. A sleeve extends from the edge 17 ineach of the two directions, an upper expansion sleeve 18 being slippedover the guide piston 7 and a lower expansion sleeve 19 likewiseextending in sleeve form in the direction of the lower mass. In order toavoid the spring assemblies 11 being blocked together, if strongvibration occurs the ends of the expansion sleeves 18, 19 can butt ontothe respective spring plates 12 before the spring turns touch oneanother. An excessive impact load on the machine is thereby avoided. Inorder to ensure a corresponding damping capacity of the piston guide 16,the latter is produced in one piece from polyurethane. In order toreinforce the edge 17, in particular to avoid the piston guide 16 beingdamaged by the spring assemblies 11 resting on it, it is possible toinsert thin steel disks between the edge 17 and the associated springs11.

The piston guide 16 is screwed on the guide piston 7 via a trapezoidalthread 20. The trapezoidal thread 20 ensures contact over a large areabetween the piston guide 16 and the guide piston 7, so that the localsurface pressure can be kept low.

For the prevention of rotation, there is formed inside the lowerexpansion sleeve 19 an inner hexagon 21, into which a steel piece 22having an outer hexagon can be pushed and can be fixed to the guidepiston 7 by means of a screw 23. This arrangement ensures that, when themachine is in operation, the piston guide 16 cannot independentlyunscrew itself down from the guide piston 7.

The invention was explained above in terms of a tamping machineaccording to the invention for soil compaction. Furthermore, theinvention may likewise be used highly advantageously in a hammer, forexample a compression hammer, since percussion generation in the hammeris based on the same principle as in the tamping machine. The fact that,in the hammer, a pneumatic spring percussion unit is normally usedinstead of the steel springs forming the spring assemblies 11 has noinfluence on the positive effects of the embodiment according to theinvention.

A weight saving of several kilograms can be achieved by using plastics.However, this saved weight may also be added to the upper mass, so thatthe latter increases in mass, as compared with devices known from theprior art. The upper mass consequently becomes quieter during operation,with the result that fewer hand-arm vibrations are transmitted to theoperator. The overall mass of the tamper remains constant, as comparedwith when the relevant components are produced from steel.

1. A tamping machine for soil compaction, comprising: a working masswhich is driven in a tamping manner and which can be driven linearlyback and forth, via a crank mechanism and a spring assembly, by a motorbelonging to an upper mass, wherein the crank mechanism has at least onestructural element which is moveable linearly back and forth and whichis produced from a material, the density of which is lower than that ofsteel, and wherein the structural element which is moveable linearlyback and forth is a structural element from the group comprising aconnecting rod, a piston pin, a guide piston, and a piston guide.
 2. Thetamping machine as claimed in claim 1, wherein the material is analuminum alloy.
 3. The tamping machine as claimed in claim 1, whereinthe material is a plastic.
 4. The tamping machine as claimed in claim 1,wherein the piston guide is produced from plastic in one piece togetherwith at least one dampening bushing.
 5. A tamping machine for soilcompaction, comprising: a working mass which is linearly reciprocatablein a tamping direction to tamp soil; a crank mechanism and a springassembly which drive said working mass to linearly reciprocate in thetamping direction; and an upper mass including a motor operativelycoupled to the crank mechanism; wherein the crank mechanism has at leastone structural element which is linearly reciprocatable and which isproduced from a material having a density lower than that of steel, andwherein the structural element comprises at least one of a connectingrod, a piston pin, a guide piston, and a piston guide.
 6. The tampingmachine as claimed in claim 5, wherein the material is an aluminumalloy.
 7. The tamping machine as claimed in claim 5, wherein thematerial is a plastic.
 8. The tamping machine as claimed in claim 5,wherein the piston guide is produced from plastic in one piece togetherwith at least one dampening bushing.